Combination additive for mineral lubricating oils



limited States Patent CONIBINATION ADDITIV E FOR MINERAL LUBRICATING OILS Elmer B. Cyphers, Cranford, and Raymond P. Nejak, Elizabeth, N. 3., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application July 29, 1953, Serial No. 371,142

2 Claims. (Cl. 25237.5)

The present invention relates to mineral lubricating oil compositions containing a combination additive for imparting improved detergency characteristics thereto. It particularly relates to a combination additive containing certain oil soluble metal naphthenates and phenolic materials having improved detergency characteristics.

It is conventional to employ metal salts of various inorganic compounds as additives for mineral oil compositions employed to lubricate internal combustion engines.

Such additives are needed to reduce the formation of harmful deposits such as varnish and the like on various engine parts and to maintain deposit-forming materials in suspension in the oil. Such metal-containing materials are, however, frequently harmful when used in lubricants for high powered internal combustion engines such as aviation engines and the like. This is because the high powered engines are subject to a phenomenon known as preignition which is the initiation of fuel combustion before the spark is delivered. Apparently the difliculty arises when metal-containing additives find their way into the combustion chamber, break down into ash, and the ash deposits like stalactite-formations on various engine parts. The points of these formations may glow at temperatures above fuel combustion temperatures resulting in hot spots that will ignite the fuel during the compression stroke, resulting in abnormally high temperatures that eventually lead to destruction or damage to various engine parts.

In view of these considerations, the type of detergent additive employed in such lubricants must be selected with great care in order to utilize materials that will either form no ash or that will form ash that is innocuous as far as preignition difiiculties are concerned. On the other hand, it is likewise necessary that the detergent additives perform their function in helping to maintain the engine in a relatively clean condition.

In accordance with the present invention, mineral lubricating oil compositions are composited with small amounts of zinc or magnesium naphthenates or their mixtures in combination with a bisphenol having at least 8 carbon atoms in alkyl substituent groups. This combination of additives has been found to give unexpectedly superior performance in reducing overall engine deposits. It is particularly superior in reducing harmful engine deposits in the ring zone of the engine and in reducing coke on the piston underhead and in the rocker box of the valve mechanism. Since the amount of metal introduced into the lubricant is comparatively small, and since Zn and Mg ashes are both relatively innocuous even in moderate quantities, the ash formed in use has no harmful effect. The danger of preignition difficulties is therefore greatly reduced.

The improvements obtained with the present combination of additives are unexpected and can not be explained at this time. The use of bisphenols as anti-oxidant additives is well known, but it has not been appreciated that they, in combination with small amounts of the metal naphthenates contemplated herein, would give improved ice detergency performance in high powered internal combus tion engines. It is particularly noteworthy that the components cooperate to give synergistic improvements in ring zone deposits and the like that would not be predicted from the relatively mild potency of the individual components in these respects.

The invention will be more fully understood by reference to the following example. This example is given for the purpose of illustration only and is not to be construed as limiting the scope of the invention in any way.

Example.-Aviation CFR engine evaluations Various individual additives, alone and in combinanaphthenate and the bisphenol in another case. The zinc and magnesium naphthenates were derived from conventional petroleum naphthenic acids having an average molecular weight of about 240.

The engine tests were carried out inan aviation CFR engine. This engine is fully described in ASTM manual of engine test methods. It was operated for 25 hours at 1800 R. P. M. and 4-brake horsepower for the tests of the present invention. The oils were rated on a demerit system wherein a perfectly clean surface is given a rating of 0 and a rating of 10 is given to the worst condition that could be expected of the engine.

The results are shown in the following table.

TABLE Engine Deposit Demerits Wt. Percent Additive in Aviation Oil Ring Piston Over- Ring Stick- Var- Underall Zone ing nish head Coke 1 None 2.0 3. 9 2. 5 2. 3 3.0 1% Bis Phenol 1. 4. 3. 3 0. 8 2. 8 1. 0 0.25% Bis Phenol 2. O 4. 5 1.1 2. 3 2. 0 0.4% Zinc Naphthenate. 1. 1 2.8 0 1.1 1. 0 0.4% Zinc Naphthenate+ 0.25% Bis Phenol 0. 9 1.8 0 1. 1 0. 5 1.1% Magnesium Naphthenate+0.25% Bis Phenol... 1. 22 2. 6 0 2. 6 0.75

1 Piston underhead coke in this engine generally correlates with rocker box coke in larger engines.

The combination additives of the present invention were extremely etlective in reducing substantially all categories of engine deposit demerit. It is noted in the case of the zinc naphthenate-containing blends that overall engine deposits were reduced by a greater extent than could be predicted from the performance of the individual additives in the same concentration. This observation applies particularly to ring zone deposits. Piston underhead coking demerit was very low for the combination additive. This demerit gives an indication of rocker box coking tendencies of the oils. It should be mentioned that rocker box coking has been an extremely limiting factor in the time between overhauls of the engine in high powered reciprocating aviation engines.

It is likewise noted that the amount of zinc naphthenate needed in combination with the bisphenol to give acceptable performance was only about 0.4% by weight which is equivalent to an ash content of about 0.05 weight percent. This amount of ash has been found not to be conducive to pre-ignition ditficulties of the type mentioned heretofore. It has also been found that magnesium naphthenates are suitable as regards preignition, butare less preferred than zinc naphthenates in this invention because of their somewhat lower detergency.

The zinc or magnesium salts of naphthenic acids em ployed in the present invention may be derived from mixtures of naphthenic acids derived from various pe troleum fractions. The naphthenic acids may have average molecular weights in the range of about 150 to 350; particularly 200 to 300, although lower or higher molecular Weight materials may also be used. The zinc and magnesium salts may be prepared by well known means such as byreacting a basic inorganic compound of either zinc ormagnesium with the naphthenic acidunder conventional. qndit q s, h zinc napht na e re p ferred although magnesium naphthenates. or mixtures. of zinc and magnesium naphthenate salts may be used. The metal naphthenates are generally blended in the oil} in amounts in the range of about 0.1 to 5.0% by weight, based on the total composition. Amounts in the range of about 0.2 to 2.0% of active ingredient are generally preferred in order to maintain the total ash content ofthe lubricant at' a low level.

The alkyl bisphenols used in combination with the naphthenates may be any of the conventional bis-phenols known to the art. The bisphenols should have at least a total of 8 carbon atoms and preferably have in the range of to 30 carbon atoms in alkyl' side chains. Typical bisphenols of this type are disclosed and described in the literature such as U. S. 2,515,907 and 2,515,908, both to Stevens et a1. Specific bi'sphenols that are suitable in the combination additive include 4,4- isopropylidene-di-o-creso1; 4,4'isoproplylidene bis (Z-isopropylphenol); 2,2 bis(Z-hydroxy-3-tert.-butyl-5methoxy phenyl) propane, and particularly 2,2 -methylene bis (4-methyl-6-tert.-butyl phenol).

The amount of the bisphenol employed in the lubricant composition will generally be an amount in. the range of about 0.05 to 2.5% by weight, preferably about 0.1 to 1% by Weight based on the total composition. It will be desired to have sufficient bisphenol present to cooperate with the naphthenate salt in performing detergency functions. On the other hand, the upper limits of the amount of the 'bisphenol will be restricted to some extent by its solubility in the oil base stock. For these reasons, bisphenols having at least 8 carbon atoms in alkyl groups are generally preferred since they are more readily soluble in conventional mineral oil base stocks than are those having fewer carbon atoms in alkyl groups.

The lubricating oil base stocks used in the compositions of this invention may be straight mineral lubricating oils or distilla'tes derived from parafiiuic, naphthenic, asp'haltic or mixed base crudes, or, if desired, various blended oils may be employed. as. well as residuals, particularly those from which asphal'tic constituents have been carefully removed. The base, stocks will usually range from about 40 to 150 seconds (Saybolt) viscosity at 210 F. The viscosity index may range from 0 to or even higher; although for aviation lubricants, which are the preferred base stocks in the practice of the present invention, the higher viscosity indexes are preferred.

What is claimed is:

1. A lubricant composition consisting essentially of a parafiin-base lubricating oil, in the range of about 0.1 to 1.0% by weight of 2,2'-methylenebis (4-methyl-6tert.- butylphenol) and. in, the range of 0.2 to 2.0% by weight of zinc naphthenate obtained from petroleum naphthenic. acids having an average molecular weight in the range of abou .00 to 300..

2. A composition as in claim 1 wherein said naphthenic acids have an average molecular weight ofabout 240.

2,515,908 Stevens et al July 18, 1950 Parker May 14, 193-5 Raymond Nov. 6, 1945 

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A PARAFFIN-BASE LUBRICATING OIL, IN THE RANGE OF ABOUT 0.1 TO 1.0% BY WEIGHT OF 2,2''-METHYLENBIS (4-METHY-6-TERT.BUTYLPHENOL) AND IN THE RANGE OF 0.2 TO 2.0% BY WEIGHT OF ZINC NAPHTHENATE OBTAINED FROM PETROLEUM NAPTHENIC ACIDS HAVING AN AVERAGE MOLECULAR WEIGHT IN THE RANGE OF ABOUT 200 TO
 300. 